Capacitive cordless writing device

ABSTRACT

When a touch sensor is approached or touched by a capacitive pen in a small area, the corresponding approach or touch signal might be slightly less than the threshold originally used for normal detection. By comparing the sum of the corresponding approach or touch signal and some adjacent signals with the threshold, the approach or touch of a small-area object that otherwise would not be detected by the original method can be determined. The capacitive pen can be made of bonded conductive fibers.

CROSS REFERENCE TO RELATED PATENT APPLICATION

This patent application claims the domestic priority of the U.S.provisional application 61/577,175 filed on Dec. 19, 2011, and herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a capacitive writing device, and moreparticularly, to a cordless capacitive writing device in phase with atouch sensor.

2. Description of the Prior Art

A conventional mutual capacitive sensor is shown includes an insulatingsurface layer, a first conductive layer, a dielectric layer, a secondconductive layer. The first conductive layer and the second conductivelayer have a plurality of first conductive strips and a plurality ofsecond conductive strips, respectively. Each of these conductive stripscan be made up by a plurality of conductive pads and connecting lines 19connected to the conductive pads in series.

In the process of mutual capacitive detection, one of the firstconductive layer and the second conductive layer is driven, while theother of the first conductive layer and the second conductive layer isdetected. For example, a driving signal is sequentially provided to eachfirst conductive strip, and corresponding to each first conductive stripprovided with the driving signal, signals from all of the secondconductive strips are detected, which represent capacitive couplingsignals at the intersections between the first conductive strip providedwith the driving signal and all the second conductive strips. As aresult, capacitive coupling signals at the intersections between all thefirst and second conductive strips are obtained to form an image ofcapacitive values.

The image of capacitive values at the time when there is no externaltouches is obtained as a reference. By comparing the difference betweenthe reference image and the image of capacitive values later detected,the touch or approach of an external conductive object can bedetermined, and furthermore, the position touched or approached by theexternal conductive object can be determined.

However, the magnitude of this difference between the reference imageand the image of capacitive values later detected is proportional to thearea on the touch sensor approached or touched by an external conductiveobject, thus the area must be sufficiently large in order to beidentified. Such a limitation therefore dictates the size of the penhead of a passive capacitive pen to be relatively large, preferablylarger than 4 mm. The large pen head may block the view of a user fromseeing the tip of the pen during writing. As a result, writing may notbe accurately made at desired locations.

From the above it is clear that prior art still has shortcomings. Inorder to solve these problems, efforts have long been made in vain,while ordinary products and methods offering no appropriate structuresand methods. Thus, there is a need in the industry for a novel techniquethat solves these problems.

SUMMARY OF THE INVENTION

When a touch sensor is approached or touched by an object of a smallarea, the corresponding approach or touch signal might be slightly lessthan the threshold originally used for normal external conductive objectdetection. An objective of the present invention is to determine anapproach or a touch of a small-area object that otherwise would not bedetected by the original method by comparing the sum of thecorresponding approach or touch signal and some adjacent signals withthe threshold.

A conventional passive capacitive pen requires a contact area with thetouch sensor large enough to be identified. Such a limitation thereforedictates the size of the pen head of the passive capacitive pen to berelatively large, which results in low accuracy when one wishes to writeat a desired location. Another objective of the present invention istherefore to provide a writing experience closer to that of conventionalwriting on papers by allowing a cordless capacitive pen to send out asignal to the touch sensor. In this way, the pen head of the capacitivepen can be made smaller, and writing can be made more accurately on thedesired locations.

The above and other objectives of the present invention can be achievedby the following technical scheme. A method for detecting an approach ora touch of a small area proposed by the present invention includes:obtaining an image of change in capacitive coupling from a capacitivetouch sensor, wherein the capacitive touch sensor includes a pluralityof driven conductive strips driven by a driving signal and a pluralityof sensed conductive strips providing changes in capacitive coupling,each time the driving signal is provided, one or more intersectionsbetween one or more of the driven conductive strips being simultaneouslyprovided with the driving signal and each sensed conductive stripgenerate capacitive coupling, and each value in the image of change incapacitive coupling is the change in capacitive coupling for one of theintersections; detecting each detected intersection from the image ofchange in capacitive coupling, wherein the value of the detectedintersection is smaller than a first threshold and larger than a secondthreshold; detecting each first region, wherein each first regionincludes one of the detected intersections and an intersection adjacentto the detected intersection, and the sum of values of the first regionis greater than the first threshold; detecting each second region if nofirst region is detected, wherein each second region includes fouradjacent intersections including one of the detected intersections, andthe sum of values of the second region is greater than the firstthreshold; and determining a first region or a second region approachedor touched by an external conductive object when at least one firstregion or at least one second region is detected, wherein the values ofall intersections adjacent to the first region or the second regionapproached or touched by the external conductive object are all smallerthan a third threshold.

The above and other objectives of the present invention can further beachieved by the following technical scheme. A device for detecting anapproach or a touch of a small area proposed by the present inventionincludes: a means for obtaining an image of change in capacitivecoupling from a capacitive touch sensor, wherein the capacitive touchsensor includes a plurality of driven conductive strips driven by adriving signal and a plurality of sensed conductive strips providingchanges in capacitive coupling, each time the driving signal isprovided, one or more intersections between one or more of the drivenconductive strips being simultaneously provided with the driving signaland each sensed conductive strip generate capacitive coupling, and eachvalue in the image of change in capacitive coupling is the change incapacitive coupling for one of the intersections; a means for detectingeach detected intersection from the image of change in capacitivecoupling, wherein the value of the detected intersection is smaller thana first threshold and larger than a second threshold; a means fordetecting each first region, wherein each first region includes one ofthe detected intersections and an intersection adjacent to the detectedintersection, and the sum of values of the first region is greater thanthe first threshold; a means for detecting each second region if nofirst region is detected, wherein each second region includes fouradjacent intersections including one of the detected intersections, andthe sum of values of the second region is greater than the firstthreshold; and a means for determining a first region or a second regionapproached or touched by an external conductive object when at least onefirst region or at least one second region is detected, wherein thevalues of all intersections adjacent to the first region or the secondregion approached or touched by the external conductive object are allsmaller than a third threshold.

The above and other objectives of the present invention can further beachieved by the following technical scheme. A method for detecting anapproach or a touch of a small area proposed by the present inventionincludes: obtaining an image of change in capacitive coupling from acapacitive touch sensor, wherein the capacitive touch sensor includes aplurality of driven conductive strips driven by a driving signal and aplurality of sensed conductive strips providing changes in capacitivecoupling, each time the driving signal is provided, one or moreintersections between one or more of the driven conductive strips beingsimultaneously provided with the driving signal and each sensedconductive strip generate capacitive coupling, and each value in theimage of change in capacitive coupling is the change in capacitivecoupling for one of the intersections; detecting each detectedintersection from the image of change in capacitive coupling, whereinthe value of the detected intersection is smaller than a first thresholdand larger than a second threshold; detecting each first region, whereineach first region includes one of the detected intersections and anintersection adjacent to the detected intersection, and the sum ofvalues of the first region is greater than the first threshold; and whenat least one first region is detected, detecting a first regionapproached or touched by an external conductive object, wherein thevalues of all intersections adjacent to the first region approached ortouched by the external conductive object are all smaller than a thirdthreshold.

The above and other objectives of the present invention can further beachieved by the following technical scheme. A device for detecting anapproach or a touch of a small area proposed by the present inventionincludes: a means for obtaining an image of change in capacitivecoupling from a capacitive touch sensor, wherein the capacitive touchsensor includes a plurality of driven conductive strips driven by adriving signal and a plurality of sensed conductive strips providingchanges in capacitive coupling, each time the driving signal isprovided, one or more intersections between one or more of the drivenconductive strips being simultaneously provided with the driving signaland each sensed conductive strip generate capacitive coupling, and eachvalue in the image of change in capacitive coupling is the change incapacitive coupling for one of the intersections; a means for detectingeach detected intersection from the image of change in capacitivecoupling, wherein the value of the detected intersection is smaller thana first threshold and larger than a second threshold; a means fordetecting each first region, wherein each first region includes one ofthe detected intersections and an intersection adjacent to the detectedintersection, and the sum of values of the first region is greater thanthe first threshold; and a means for detecting a first region approachedor touched by an external conductive object when at least one firstregion is detected, wherein the values of all intersections adjacent tothe first region approached or touched by the external conductive objectare all smaller than a third threshold.

The above and other objectives of the present invention can further beachieved by the following technical scheme. A method for detecting anapproach or a touch of a small area proposed by the present inventionincludes: obtaining an image of change in capacitive coupling from acapacitive touch sensor, wherein the capacitive touch sensor includes aplurality of driven conductive strips driven by a driving signal and aplurality of sensed conductive strips providing changes in capacitivecoupling, each time the driving signal is provided, one or moreintersections between one or more of the driven conductive strips beingsimultaneously provided with the driving signal and each sensedconductive strip generate capacitive coupling, and each value in theimage of change in capacitive coupling is the change in capacitivecoupling for one of the intersections; detecting each intersection witha value greater than a first threshold from the image of change incapacitive coupling; and determining a single intersection of anapproach or a touch of a small area by each external conductive objectwhen at least one intersection with the value greater than the firstthreshold is detected, wherein all intersections adjacent to the singleintersection of the approach or touch of a small area by each externalconductive object are all smaller than the first threshold.

The above and other objectives of the present invention can further beachieved by the following technical scheme. A capacitive writing deviceproposed according to the present invention includes: a capacitive penincluding a conductive pen body and a conductive pen head in contactwith the conductive pen body, and the conductive pen head including acontact portion and a non-contact portion, wherein the contact portionis softer than the non-contact portion, and the conductive pen head ismade of bonded conductive fibers, some or all of which extend from thenon-contact portion to the contact portion; a touch sensor including aplurality of driven conductive strips provided with a driving signal anda plurality of sensed conductive strips providing changes in capacitivecoupling, each time the driving signal being provided, one or moreintersections between one or more of the driven conductive strips beingsimultaneously provided with the driving signal and each sensedconductive strip generating capacitive coupling; and a control circuitfor determining the location of the capacitive pen on the touch sensorbased on the changes in capacitive coupling produced at theintersections when the capacitive pen is held on the touch sensor by anexternal conductive object.

The above and other objectives of the present invention can further beachieved by the following technical scheme. A cordless capacitivewriting device proposed by the present invention may include: a touchsensor including a plurality of conductive strips including a pluralityof first conductive strips and a plurality of second conductive strips;a capacitive pen including a conductive pen head and a signal conversioncircuit, the conductive pen head for receiving a driving signal from thetouch sensor, and the signal conversion circuit for generating a delayeddriving signal after delaying a predefined period of time based on thedriving signal, the delayed driving signal being transmitted to thetouch sensor through the conductive pen head, wherein the driving signaland the delayed driving signal have the same frequency and phase; and acontroller for detecting the location of at least one externalconductive object based on a change in capacitive coupling of thedriving signal between the touch sensor and the at least one externalconductive object in a passive mode, and detecting the location of atleast one external conductive object based on the delayed driving signalreceived from the capacitive pen in an active mode.

With the above technical schemes, the present invention achieve at leastthe following advantages and beneficial effects:

1. The approach or touch of a pen head with an area smaller thantraditional capacitive pens can be detected;

2. The approach of an external conductive object with a smaller areasuspending in the air can be detected; and

3. Writing can be made more accurately at the expected locations, whichprovides a writing experience more similar to that of conventionalwriting on papers.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thefollowing detailed description of the preferred embodiments, withreference made to the accompanying drawings, wherein:

FIGS. 1A and 1B are schematic diagrams illustrating a mutual capacitivesensor;

FIGS. 1C to 1E are schematic diagrams illustrating a touch sensorapproached or touched by a capacitive pen with a small pen headaccording to a first embodiment of the present invention;

FIGS. 1F to 1G are schematic diagrams illustrating determining of anapproach or a touch by a capacitive pen with a small pen head accordingto the first embodiment of the present invention;

FIG. 2A is a flowchart illustrating detecting of an approach or a touchof a small area according to the first embodiment of the presentinvention;

FIGS. 2B to 2G are schematic diagrams illustrating a first region and asecond region according to the first embodiment of the presentinvention;

FIGS. 3A and 3B are schematic diagrams illustrating a capacitive penproposed by a second embodiment of the present invention;

FIGS. 4A and 4B are schematic diagrams illustrating the operating of acapacitive pen proposed by a third embodiment of the present invention;

FIG. 4C is a schematic diagram illustrating a shielding conductive stripproposed by the third embodiment of the present invention; and

FIG. 4D is a schematic diagram illustrating a circuit for phasesynchronization proposed by the third embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some embodiments of the present invention are described in detailsbelow. However, in addition to the descriptions given below, the presentinvention can be applicable to other embodiments, and the scope of thepresent invention is not limited by such, rather by the scope of theclaims. Moreover, for better understanding and clarity of thedescription, some components in the drawings may not necessary be drawnto scale, in which some may be exaggerated relative to others, andirrelevant parts are omitted.

Referring to FIG. 1A, the present invention provides a positiondetecting device 100, which includes a sensing device 120 and adriving/detecting unit 130. The sensing device 120 has a sensing layer.In an example of the present invention, the sensing layer can include afirst sensing layer 120A and a second sensing layer 120B. The first andsecond sensing layers 120A and 120B each has a plurality of conductivestrips 140, wherein the first conductive strips 140A of the firstsensing layer 120A and the second conductive strips 140B of the secondsensing layer 120B cross each other. In another example of the presentinvention, the first and second conductive strips 140A and 140B aredisposed on a co-planar sensing layer. The driving/detecting unit 130produces sensing information based on signals of the conductive strips140. In the case of self-capacitive detection, for example, conductivestrips 140 that are being driven are detected. In the case ofmutual-capacitive detection, some of the conductive strips 140 that arenot being directly driven by the driving/detecting unit 130 aredetected. In addition, the sensing device 120 can be disposed on adisplay 110. An optional rear shielding layer (not shown) can beinterposed between the sensing device 120 and the display 110. In apreferred example of the present invention, there is no rear shieldinglayer between the sensing device 120 and the display 110 so as to reducethe thickness of the sensing device 120.

The first and second conductive strips can be a plurality of columnconductive strips and row conductive strips arranged in columns androws; a plurality of first dimensional conductive strips and seconddimensional conductive strips arranged in first and second dimensions;or a plurality of first axial conductive strips and second axialconductive strips arranged in first and second axes. In addition, thefirst and second conductive strips can be arranged in orthogonal ornon-orthogonal directions. For example, in a polar coordinate system,one of the first and second conductive strips can be arranged in radialdirection, and the other one of the first and second conductive stripscan be arranged in circular direction. Furthermore, one of the first andsecond conductive strips can be driving conductive strips, while theother one of the first and second conductive strips can be detectingconductive strips. Said “first dimension” and “second dimension”, “firstaxis” and “second axis”, “driving” and “detecting”, “driven” or“detected” conductive strips can be used to mean said “first and“second” conductive strips, including but not limited to, being arrangedin orthogonal grids, and in any other geometric configurationscomprising first dimensional and second dimensional intersectingconductive strips.

The position detecting device 100 of the present invention can beapplied to a computing system as shown in FIG. 1B, which includes acontroller 160 and a host 170. The controller includes thedriving/detecting unit 130 to operatively couple the sensing device 120(not shown). In addition, the controller 160 can include a processor 161for controlling the driving/detecting unit 130 in generating the sensinginformation. The sensing information can be stored in a memory 162 andaccessible by the processor 161. Moreover, the host 170 constitutes themain body of the computing system, and mainly includes a centralprocessing unit 171, a storage unit 173 that can be accessed by thecentral processing unit 171, and the display 110 for displaying resultsof operations.

In another example of the present invention, there is a transmissioninterface between the controller 160 and the host 170. The controllingunit transmits data to the host via the transmission interface. One withordinary skill in the art can appreciate that the transmission interfacemay include, but not limited to, UART, USB, I2C, Bluetooth, Wi-Fi, IRand other wireless or wired transmission interfaces. In an example ofthe present invention, data transmitted can be positions (e.g.coordinates), identified results (e.g. gesture codes), commands, sensinginformation or other information provided by the controller 160.

In an example of the present invention, the sensing information can beinitial sensing information generated under the control of the processor161, and this information is passed onto the host 170 for positionanalysis, such as position analysis, gesture determination, commandidentification, and so on. In another example of the present invention,the sensing information can be analyzed by processor 161 first beforeforwarding the determined positions, gestures, commands, or the like tothe host 170. The present invention does not limit to this example, andone with ordinary skill in the art can readily recognize otherinteractions between the controller 160 and the host 170.

At each intersection of the conductive strips, the upper and lowerconductive strips form the positive and negative electrodes. Eachintersection can be regarded as one pixel in an image. When one or moreexternal conductive objects approach or touch the sensing device, saidimage can be regarded as a photographed touch image (e.g. the pattern ofa finger upon touching the sensing device).

When a driven conductive strip is being provided with a driving signal,the driven conductive strip itself produces self capacitance, andproduces mutual capacitance on each intersection of the drivenconductive strip. Said self-capacitive detection is detecting theself-capacitance of all the conductive strips, which is particularlyuseful in determining approach or touch of a single external conductiveobject.

In said mutual-capacitive detection, when a driven conductive strip isbeing provided with a driving signal, capacitances or changes incapacitances of all intersections on the driven conductive strip aredetected with all sensed conductive strips arranged in differentdimensions to the driven conductive strip, and are regarded as a row ofpixels. Accordingly, all the rows of pixels are combined to form saidimage. When one or more external conductive objects approach or touchthe sensing device, said image can be regarded as a photographed touchimage, which is particularly useful in determining approaches or touchesof a plurality of external conductive objects.

These conductive strips (the first and second conductive strips) can bemade of transparent or opaque materials, such as transparent Indium TinOxide (ITO). In terms of the structure, it can be categorized into aSingle ITO (SITO) structure and a Double ITO (DITO) structure. One withordinary skill in the art can appreciate that other materials can beused as the conductive strips, such as carbon nanotube, and they willnot be further described.

In an example of the present invention, the horizontal direction isregarded as the first direction, while the vertical direction isregarded as the second direction. Thus, the horizontal conductive stripsare the first conductive strips, and the vertical conductive strips arethe second conductive strips. However, one with ordinary skill in theart can appreciate that the above is merely an example of the presentinvention, and the present invention is not limited to this. Forexample, the vertical direction can be regarded as the first direction,while the horizontal direction can be regarded as the second direction.

During 2D mutual capacitive detection, alternating driving signals aresequentially provided to each first conductive strip, and 1D sensinginformation corresponding to each driven first conductive strip isobtained from the signals of the second conductive strips. Sensinginformation of all the first conductive strips are combined together toform 2D sensing information. 1D sensing information can be generatedbased on the signal of a second conductive strip, or based on thedifference between the signal of a conductive strip and a referencevalue. In addition, the sensing information can be generated based oncurrent, voltage, level of capacitive coupling, amount of charge orother electrical characteristics, and can be in analog or digital form.

When there is no external object actually approaching or covering thetouch screen, or when the system has not determined any external objectactually approaching or covering the touch screen, the positiondetecting device may generated a reference value based on the signals ofthe second conductive strips. This reference value represents straycapacitance on the touch screen. Sensing information can be generatedbased on the signal of a second conductive strip or the result ofsubtracting the reference value from the signal of the second conductivestrip.

In the prior art, capacitive pens are often used as an extension for thehands. The contact area of the pen with the touch screen has to be aboutthe same as that of a finger with the touch screen under normalcircumstances in order to obtain sufficient changes in signals and tocorrectly determine the position of the touch. This area should coverthe intersections of several conductive strips.

Referring to FIGS. 1C to 1E, a capacitive pen with a small pen headaccording to a first embodiment is shown. The pen head and the pen bodyof the capacitive pen P are in contact with each other, such that a handholding the pen body can be capacitive coupled to a touch screen via thepen head. In addition, the diameter of the contact area of the pen headof the capacitive pen P with the touch screen is less than about 3 mm.In a preferred example of the present invention, the diameter of thecontact area of the pen head of the capacitive pen P with the touchscreen is about 2.2 mm. During mutual capacitive detection, when adriving signal (e.g. a pulse-width modulation (PWM) signal) is providedto a first conductive strip (e.g. a first conductive strip Tx1 or Tx2),changes in capacitive coupling at each intersection on the firstconductive strip is detected through each second conductive strip (e.g.a second conductive strip Rx2) intersecting the first conductive strip.When the capacitive pen P approaches or touches an intersection (e.g.the intersection of the first conductive strip Tx2 and the secondconductive strip Rx2), the detected change in capacitive coupling V1 maybe larger than a first threshold T1. However, if the capacitive pen Pmoves to a place between two intersections (e.g. between theintersection of the first conductive strip Tx1 and the second conductivestrip Rx2 and the intersection of the first conductive strip Tx2 and thesecond conductive strip Rx2), then the changes in capacitive coupling V2and V3 at the two intersections may be lower than the first thresholdT1. As a result, the position of the pen cannot be determined.

In view of this, referring to FIGS. 1F and 1G, the present inventionproposes that when the change in capacitive coupling at an intersectionis larger than a second threshold but lower than the first threshold,then by determining whether the sum of the changes in capacitivecoupling at adjacent intersections (e.g. V23 or V32) is larger than athreshold, it is determined whether the position of the capacitive pen Pis between intersections.

In an example of the present invention, the sum of the changes incapacitive coupling at adjacent intersections may include the sum of thechanges in capacitive coupling for one or more adjacent intersections onthe same driven conductive strip (first conductive strip). For example,when a first conductive strip is provided with a driving signal, sensinginformation corresponding to this first conductive strip is formed fromthe changes in capacitive coupling detected from a plurality ofconsecutive second conductive strips. If a value in the sensinginformation is larger than the second threshold but less than the firstthreshold, then this value in the sensing information and a previous ora subsequent value is added together for comparing with the firstthreshold.

In another example of the present invention, sensing information (1Dsensing information) corresponding to a plurality of conductive stripsform an image (2D sensing information). Each value in the sensinginformation that is larger than the second threshold but less than thefirst threshold is the sum of the changes in capacitive coupling atadjacent intersections in the image.

Moreover, referring to FIG. 2A, a method for detecting a capacitive penwith a small pen head according to this embodiment is shown. As shown instep 210, an image of change in capacitive coupling is obtained. Morespecifically, first, an image can be obtained when the touch screen isnot approached or touched by any external object. This image is used asa reference image. Then, images are obtained one or several consecutivetimes. The difference between each obtained image and the referenceimage is the image of change in capacitive coupling. Values of the imageof change in capacitive coupling correspond to a plurality of drivenconductive strips (first conductive strips). A value corresponding toeach driven conductive strip is generated based on a plurality of sensedconductive strips. Each driven conductive strip (e.g. a first conductivestrip) and sensed conductive strip (e.g. a second conductive strip) maycorrespond to a horizontal coordinate and a vertical coordinate,respectively. Each time a driving signal is provided to a drivenconductive strip, the coordinates of each intersection on the drivenconductive strip is a 2D coordinate intersected by overlapping drivenconductive strip and sensed conductive strip. The 2D coordinate can bewritten, for example, as (coordinate of the driven conductive strip,coordinate of the sensed conductive strip).

In an example of the present invention two or more adjacent drivenconductive strips can be driven simultaneously. For example, when thereare N first conductive strips, the driving signal is provided to twoadjacent first conductive strips simultaneously at a time, and at leastone of the two first conductive strips is not the same between eachdriving. The conductive strips are driven N−1 times. Compared to theexample of driving only one first conductive strip each time thatgenerates an image of change in capacitive coupling (2D sensinginformation) consisting of N 1D sensing information, driving twoadjacent first conductive strips simultaneously at a time will generatean image of change in capacitive coupling consisting of N−1 1D sensinginformation. In this example, the coordinates for each intersection areeffectively a 2D coordinate consisting of the coordinate at the middleof two adjacent driven conductive strips and the coordinate of a sensedconductive strip.

Next, in step 220, each intersection with a value smaller than a firstthreshold and larger than a second threshold is detected as a detectedintersection. Then, in step 230, each first region is detected, whichincludes the detected intersection and an adjacent intersection. Thedetected intersection and the adjacent intersection correspond todifferent driven conductive strips. The sum of the values of the firstregion (sum of the detected intersection and the adjacent intersection)is larger than the first threshold. Next, in step 240, each secondregion is detected. The second region encompasses four intersections(including the detected intersection and three other intersections).Each intersection in the second region is adjacent to two otherintersections in the second region, and the sum of the values of thesecond region (sum of the detected intersection and the other threeintersections) is larger than the first threshold. In an example of thepresent invention, the second region is detected if no first region isdetected. In another example of the present invention, the second regionis detected regardless of whether a first region is detected or not. Instep 250, when values of intersections adjacent to or neighboring thefirst region or the second region are all smaller than a thirdthreshold, then the first or second region is determined to be a regionapproached or touched by an external conductive object.

Referring to FIGS. 2B to 2G, the matrix shown indicates intersections(intersection 00, intersection 01, . . . intersection 04, intersection10, intersection 11, . . . intersection 44) of five first conductivestrips (driven conductive strips) and five second conductive strips(sensed conductive strips), wherein the intersections 00, 01, 02, 03 and04 are intersections on the first conductive strip T0; the intersections10, 11, 12, 13 and 14 are intersections on the first conductive stripT1; and so on.

Under the assumption that the intersection 22 is detected as thedetected intersection in step 220, then in step 230, possible firstregions are shown in FIGS. 2B and 2C, which include the intersections 12and 22, and the intersections 22 and 32, respectively. If the sum ofvalues of the intersections 12 and 22 is greater than the firstthreshold, then the intersections 12 and 22 are detected as the firstregion. Alternatively, if the sum of values of the intersections 22 and32 is greater than the first threshold, then the intersections 22 and 32are detected as the first region. On the contrary, if neither the sum ofvalues of the intersections 12 and 22 nor the sum of values of theintersections 22 and 32 is greater than the first threshold, then nofirst region is detected.

Furthermore, in step 240, possible second regions are shown in FIGS. 2Dto 2G, which include the intersections 11, 12, 21 and 22 in FIG. 2D; theintersections 12, 13, 22 and 23 in FIG. 2E; the intersections 21, 22, 31and 32 in FIG. 2F; and the intersections 22, 23, 32 and 33 in FIG. 2G.If the sum of values of the four intersections in any of FIGS. 2D to 2Gis greater than the first threshold, then a second region is detected.Otherwise, if none of the sum of values of the four intersections inFIGS. 2D to 2G is greater than the first threshold, no second region isdetected.

In addition, in step 250, assuming the first region is detected as shownin FIG. 2B, then in an example of the present invention, the neighboringintersections of the first regions can be intersections 02, 11, 13, 21,23 and 32; in another example of the present invention, the neighboringintersections of the first regions can be intersections 01, 02, 03, 11,13, 21, 23, 31, 32 and 33. The neighboring intersections of the regionsshown in FIGS. 2C to 2G can be similarly deduced, and will not befurther explained.

Moreover, in a best mode of the present invention, the second thresholdand the third threshold are ½ and ¼ of the first threshold,respectively, and wherein the first threshold>the second threshold>thethird threshold. One with ordinary skill in the art can appreciate otherfirst, second and third threshold values; the present invention is notlimited to the magnitudes described herein.

In a preferred example of the present invention, the pen head of thecapacitive pen is thin with a width between about 2 mm˜3 mm, which isless than the minimum gap between two parallel conductive strips or twoparallel driven conductive strips. For example, the width of the penhead is less than the gap between the center of a conductive strip andthe center of another conductive strip, or less than the gap between thecenter of a first conductive strip and the center of another adjacentfirst conductive strip.

An algorithm provided based on FIG. 2A is as follows. DD[i][j] indicatesan intersection detected in step 220.

if( g_ComtParam.m_Ctrl & CTRL_PEN_DETECTION ) {   if( DD[i][j] > 0 )   {    for( m = −1; m <= 1; m+=2 )     {       if( DD[i+m][j] >TOUCHTHRESHOLD/2 )       {         Sum = DD[i][j] + DD[i+m][j];        if( Sum >= TOUCHTHRESHOLD )         {           if( DD[i][j−1]<= TOUCHTHRESHOLD/4 && DD[i][j+1] <= TOUCHTHRESHOLD/4 && DD[i+m][j−1] <=TOUCHTHRESHOLD/4 && DD[i+m][j+1] <= TOUCHTHRESHOLD/4 && DD[i+2*m][j] <=TOUCHTHRESHOLD/4 && DD[i−m][j] <= TOUCHTHRESHOLD/4 )           {bDetected = 1;    //signal is detected             gotoEndDetectLinePcs;           }         }       }       for( n = −1; n <=1; n+=2 )       {         if( DD[i][j+n] >= 0 &&           DD[i+m][j] >=0 &&           DD[i+m][j+n] >= 0 )         {           Sum = DD[i][j]+                DD[i][j+n]+                 DD[i+m][j]+                DD[i+m][j+n];           if( Sum >= TOUCHTHRESHOLD )          {             if( DD[i][j+2*n] <=             TOUCHTHRESHOLD/4&&               DD[i][j−n] <=               TOUCHTHRESHOLD/4 &&              DD[i+m][j+2*n]<= TOUCHTHRESHOLD/4 &&              DD[i+m][j−n] <= TOUCHTHRESHOLD/4 &&              DD[i+2*m][j+n] <= TOUCHTHRESHOLD/4 &&              DD[i+2*m][j] <= TOUCHTHRESHOLD/4 &&              DD[i−m][j+n] <= TOUCHTHRESHOLD/4 &&              DD[i−m][j] <= TOUCHTHRESHOLD/4 )             {              bDetected = 1;   //  signal is detected               gotoEndDetectLinePcs;             }           }         }       }     }   }}

Based on the descriptions above, the present invention provides a devicefor detecting an approach or a touch of a small area. According to step210 above, the present invention includes a means for obtaining an imageof change in capacitive coupling from a capacitive touch sensor. Thecapacitive touch sensor includes a plurality of driven conductive stripsdriven by a driving signal and a plurality of sensed conductive stripsproviding changes in capacitive coupling. Each time the driving signalis provided, one or more intersections between one or more of the drivenconductive strips being simultaneously provided with the driving signaland each sensed conductive strip generate capacitive coupling. Eachvalue in the image of change in capacitive coupling is the change incapacitive coupling for one of the intersections.

According to step 220, the present invention includes a means fordetecting each detected intersection from the image of change incapacitive coupling, wherein the value of the detected intersection issmaller than a first threshold and larger than a second threshold.

According to step 230, the present invention includes a means fordetecting each first region, wherein each first region includes one ofthe detected intersections and an intersection adjacent to the detectedintersection, and the sum of values of the first region is greater thanthe first threshold.

According to step 240, the present invention includes a means fordetecting each second region, wherein each second region includes fouradjacent intersections including one of the detected intersections, andthe sum of values of the second region is greater than the firstthreshold. As described before, the second region is detected only if nofirst region is detected. Alternatively, the second region is detectedregardless of whether first region is detected or not.

According to step 250, the present invention includes a means fordetermining a first or second region approached or touched by anexternal conductive object when at least one first region or at leastone second region is detected, wherein the values of all intersectionsadjacent to the first region or the second region approached or touchedby the external conductive object are all smaller than a thirdthreshold.

The above touch sensor may include a plurality of driven conductivestrips driven by a driving signal and a plurality of sensed conductivestrips providing changes in capacitive coupling. Each time the drivingsignal is provided, one or more intersections between one or more of thedriven conductive strips being simultaneously provided with the drivingsignal and each sensed conductive strip generates capacitive coupling.Based on the capacitive coupling, the sensed conductive strips providechanges in capacitive coupling for the intersections. Each value in theimage of change in capacitive coupling is the change in capacitivecoupling for one of the intersections.

As described before, in an example of the present invention, the firstthreshold>the second threshold>the third threshold. For example, thesecond threshold is ½ of the first threshold, and the third threshold is¼ of the first threshold. In addition, in a best mode of the presentinvention, the maximum width of the approach or touch of a small area isless than or equal to the gap between the centers of two adjacentconductive strips. For example, the maximum width of the approach ortouch of a small area is less than or equal to 3 mm, and the gap betweenthe centers of two adjacent conductive strips is below 6.5 mm. The twoadjacent conductive strips may be two driven conductive strips or sensedconductive strips arranged adjacent and in parallel with each other.

The above maximum width of the approach or touch of a small area meansthe maximum width of an applicable range for detecting an approach or atouch of a small area used by the touch sensor of the present invention,rather than the maximum width for detecting an approach or a touch of anexternal conductive object by the touch sensor of the present invention.When the approach or touch of an external conductive object is largerthan the maximum width of an approach or a touch of a small area, normaldetecting method can be used for detecting. For example, detectingwithout determining the first region or the second region. As such, thepresent invention may detect the approach or touch of ordinary externalconductive objects, and also detect the approach or touch of externalconductive objects with small areas. For example, when the externalconductive object is a pen, the coupled area on the touch sensor causedby a touch or an approach of the pen is less than or equal to the abovemaximum width of an approach or a touch of a small area. As anotherexample, when an external conductive object approaches (suspends in theair) above the touch sensor, the area of capacitive coupling between theexternal conductive object and the touch sensor would be relativelysmaller than the area of capacitive coupling with the touch sensor whilethe external conductive object is touching the touch sensor. When thearea of capacitive coupling on the touch sensor which an externalconductive object is capable of causing is less than or equal to theabove maximum width of an approach or a touch of a small area, it can beregarded as the approaching of an external conductive object of a smallarea.

Accordingly, an example of the present invention further includes:detecting each intersection with a value larger than a first thresholdfrom an image of change in capacitive coupling, and when at least oneintersection with a value larger than the first threshold is detected,determining a single intersection of an approach or a touch of a smallarea for each external conductive object, wherein all intersectionsadjacent to the single intersection of the approach or touch of a smallarea for each external conductive object are smaller than the firstthreshold.

In an example of the present invention, step 250 may be performed afterstep 230. Step 250 may also be performed after step 240. In anotherexample of the present invention, step 250 is performed after both steps230 and 240 are completed.

Referring to FIGS. 3A and 3B, a capacitive pen 30 proposed by a secondembodiment of the present invention is shown. The capacitive pen 30includes a conductive pen body 31 and a conductive pen head 32. Theconductive pen head is in physical contact with the conductive pen body,such that when the conductive pen body is in contact with the hand orperson holding the pen, the conductive pen head is coupled to the handor human body via the conductive pen body, and is further coupled toground through the human body. In an example of the present invention,the conductive pen head 32 is made by curing conductive fibers, forexample, by optical or thermal curing after being bonded together. Inaddition, the conductive pen head 32 further includes a contact portion33, wherein the degree of curing of the contact portion 33 is differentfrom that of other non-contact portion of the conductive pen head 32.More specifically, the contact portion 33 is softer than the non-contactportion of the conductive pen head 32. When the capacitive pen 30 isused for writing on a touch sensor 34, the contact portion 33 may deformdue to friction force or touch pressure, resulting in a deformed touchportion 35, thereby increasing its contact area. In a preferred exampleof the present invention, the diameter of contact between the contactportion 33 and the second conductive pads 34 is between 3 mm to 1 mm. Inan example of the present invention, the conductive pen head is made ofcollecting conductive fibers that extend in the same direction as theconductive pen body. In other words, each conductive fiber extends fromthe conductive pen body towards the tip of the pen; some or all of theconductive fibers extend from the non-contact portion to the contactportion. The bonding of the conductive fibers can be achieved byconductive adhesives. One with ordinary skill in the art may appreciatethe various materials of the conductive fibers (e.g. conductivepolyester, conductive polyamine etc.) and the conductive adhesives (e.g.UV cured conductive adhesives); and they will not be described indetails herein.

Moreover, the conductive pen head may further include a conductivesupport (not shown). The conductive support can be made of metal ornon-metal materials, for example, a copper rod or a graphite rod. Inaddition, the tip of the contact portion may further include a recessedportion providing a space recessed into the contact portion 33, whichgives a larger area than a non-recessed tip. The contact portion 33 maybe of a cone shape, wherein the above recess is provided at the top ofthe cone.

In an example of the present invention, the maximum width of contactbetween the contact portion 33 and the second conductive pads 34 is lessthan the distance between the center lines of two conductive stripsarranged in parallel on the touch sensor 34. In an example of thepresent invention, the contact portion 33 touches two parallelconductive strips at most. In another example of the present invention,the contact portion 33 touches two adjacent intersections at most.

Accordingly, a capacitive writing device is proposed by the presentinvention, which includes a capacitive pen, a touch sensor and a controlcircuit. The capacitive pen includes a conductive pen body and aconductive pen head in contact with the conductive pen body, and theconductive pen head includes a contact portion and a non-contactportion, wherein the contact portion is softer than the non-contactportion, and the conductive pen head is made of bonded conductivefibers, some or all of which extend from the non-contact portion to thecontact portion. In addition, the touch sensor includes a plurality ofdriven conductive strips provided with a driving signal and a pluralityof sensed conductive strips providing changes in capacitive coupling.Each time the driving signal is provided, one or more intersectionsbetween one or more of the driven conductive strips being simultaneouslyprovided with the driving signal and each sensed conductive stripgenerates capacitive coupling. Moreover, when the capacitive pen is heldon the touch sensor by an external conductive object (e.g. the hand orhuman body), the control circuit determines the location of thecapacitive pen on the touch sensor based on the changes in capacitivecoupling produced at the intersections.

Based on the device for detecting an approach or a touch of a small areadescribed above, the control circuit may include: a means for obtainingan image of change in capacitive coupling from a capacitive touchsensor, wherein each value in the image of change in capacitive couplingis the change in capacitive coupling for one of the intersections; ameans for detecting each intersection with a value greater than a firstthreshold from the image of change in capacitive coupling; and a meansfor determining a single intersection approached or touched by eachcapacitive pen when at least one intersection with the value greaterthan the first threshold is detected, wherein all intersections adjacentto the single intersection approached or touched by each capacitive penare all smaller than the first threshold.

The control circuit may further include: a means for obtaining an imageof change in capacitive coupling from a capacitive touch sensor, whereineach value in the image of change in capacitive coupling is the changein capacitive coupling for one of the intersections; a means fordetecting each detected intersection from the image of change incapacitive coupling, wherein the value of the detected intersection issmaller than a first threshold and larger than a second threshold; ameans for detecting each first region, wherein each first regionincludes one of the detected intersections and an intersection adjacentto the detected intersection, and the sum of values of the first regionis greater than the first threshold; and a means for determining a firstregion approached or touched by the capacitive pen when at least onefirst region is detected, wherein the values of all intersectionsadjacent to the first region approached or touched by the capacitive penare all smaller than a third threshold.

Furthermore, the control circuit may further include: a means fordetecting each second region if no first region is detected, whereineach second region includes four adjacent intersections including one ofthe detected intersections, and the sum of values of the second regionis greater than the first threshold; and a means for determining asecond region approached or touched by the capacitive pen when at leastone second region is detected, wherein the values of all intersectionsadjacent to the second region approached or touched by the capacitivepen are all smaller than a third threshold.

In a best mode of the present invention, the first threshold>the secondthreshold>the third threshold. For example, the second threshold is ½ ofthe first threshold, and the third threshold is ¼ of the firstthreshold.

In addition, in an example of the present invention, the maximum widthon the touch sensor by the capacitive pen is less than the distancebetween the centers of two conductive strips arranged adjacent and inparallel with each other, the two conductive strips arranged adjacentand in parallel with each other are the driven conductive strips or thesensed conductive strips. In another example of the present invention,each first region or second region determined to be approached ortouched by the capacitive pen is a first region or a second regionapproached or touched by a pen, wherein the maximum width on the touchsensor touched by the pen is less than or equal to 3 mm.

Referring to FIGS. 4A and 4B, a capacitive pen proposed by a thirdembodiment of the present invention is shown. The capacitive penincludes a conductive pen body 40 and a conductive pen head 41.Referring to FIG. 4A, when the pen head 41 is close to or in contactwith a touch sensor, the conductive pen head 41 will be capacitivelycoupled to a driven conductive strip being provided with a drivingsignal (e.g. PWM), and then based on the capacitively coupled drivingsignal, the capacitive pen provides an output signal to the touch sensorvia capacitive coupling during a period in which the driving signal isno longer provided to any driven conductive strip, as shown in FIG. 4B.The output signal will be capacitively coupled with the conductivestrips of the touch sensor to provide detected signals. For example, theoutput signal is capacitively coupled with at least one first conductivestrip Tx to provide a signal St, and with at least one second conductivestrip Rx to provide a signal Sr. By scanning the first conductive stripTx and the second conductive strip Rx, the location of the capacitivepen can be determined based on the signals St and Sr.

The capacitive pen can have a built-in power supply to provide the powernecessary for it to provide the output signal. In addition, thecapacitive pen can obtain the power required for producing the outputsignal through external electromagnetic induction. Referring now to FIG.4C, a capacitive touch sensor may include at least one shieldingconductive strip 43. In a first mode (or period), the shieldingconductive strips 43 is provided with a DC signal to shield theconductive strips from external noise interference. Further, theshielding conductive strip 43 is provided with an AC signal in a secondmode in order to form a coil that provides a magnetic field, such that acapacitive pen may obtain some or all of its required power viaelectromagnetic induction from the magnetic field produced by theshielding conductive strip 43. The number of turns on the coilsurrounding the conductive strip may be one or more. In addition, thecapacitive pen may further include a capacitive or electrical storagedevice (e.g. a battery) for storing the power received from the coil,and for providing continuous power to the capacitive pen in the absenceof the power from the coil.

FIG. 4D shows a signal conversion circuit inside the capacitive pen asmentioned before. Its main components include a first amplifier A1, anadder 45, a second amplifier A2 and a band pass filter (BPF). After thedriving signal is coupled with the conductive pen head 41, the signalbrought in by capacitive coupling is amplified by the first amplifier.In addition, the adder, the second amplifier and the BPF together forman oscillating feedback loop to provide an output signal that is inphase with the signal of the touch sensor. The output signal isoutputted from the pen head.

One with ordinary skill in the art can appreciate that the adder 45, thesecond amplifier A2 and the BPF form an oscillating feedback loop,wherein the working frequency of the oscillating feedback loop is thesame as the frequency of the driving signal. Before the driving signalis received by the oscillating feedback loop, a delayed driving signaland the driving signal may have different phases. After the drivingsignal is received by the oscillating feedback loop, the delayed drivingsignal can be made to have the same phase as the driving signal. Whenthe delayed driving signal is transmitted to the touch sensor, thecontrol circuit may detect the delayed driving signal based on the phaseof the original driving signal.

In an example of the present invention, each end of the oscillatingfeedback loop may further include a switch (switches 46 and 47)controlled by a control signal SC provided by a control circuit. Theswitches can be used to delay the output of the output signal from thepen head so as to avoid outputting it at the same time the drivingsignal is being provided. For example, the control signal can beprovided based on the output of a counter or a controller (not shown).After certain number of counts or a certain period of time, the outputsignal of the oscillating feedback loop is allowed to be outputted fromthe pen head. Accordingly, the driving signal is amplified by the firstamplifier A1 and provided to the oscillating feedback loop via theswitch 46. At this time, based on the control signal SC, the switch 46is switched on, while the switch 47 is switched off. After some time,the output signal of the second amplifier A2 in the oscillating feedbackloop will be in phase with the driving signal. Then, after a certainnumber of counts or period of time, the control signal SC controls theswitch 46 to be switched off and the switch 47 to be switched on, sothat the delayed driving signal can be outputted from the conductive penhead 41 after that certain number of counts or period of time. One withordinary skill in the art may appreciate that the receiving of thedriving signal and the outputting of the delayed driving signal can beimplemented by different electrodes, but in a best mode of the presentinvention, they are implemented by the same electrode. Also, thereceiving of the driving signal and the outputting of the delayeddriving signal by a single electrode will not occur at the same time.

According to the above, a cordless capacitive writing device is providedby the present invention, which includes: a touch sensor, a capacitivepen and a controller. The capacitive pen includes a conductive pen headand a signal conversion circuit. The conductive pen head receives adriving signal from the touch sensor. The receiving of the drivingsignal can be achieved by an electrode or a coil. The signal conversioncircuit generates a delayed driving signal after delaying a predefinedperiod of time based on the driving signal. The delayed driving signalis transmitted to the touch sensor via the conductive pen head, whereinthe driving signal and the delayed driving signal have the samefrequency and phase. The delayed driving signal may exist before thereceiving of the driving signal, but is not outputted from theconductive pen head. After receiving the driving signal, the signalconversion circuit allows the delayed driving signal to be in phase withthe driving signal, and the delayed driving signal is outputted from theconductive pen head after a certain number of counts or period of time.

The controller detects the location of at least one external conductiveobject based on the change in capacitive coupling of the driving signalbetween the touch sensor and the at least one external conductive objectin a passive mode, and detects the location of at least one externalconductive object based on the delayed driving signal received from thecapacitive pen in an active mode. In addition, in the passive mode, thecontroller detects the location of the at least one external conductiveobject at the same time the driving signal is being provided, whereas inthe active mode, the controller detects the location of the capacitivepen in the absence of the driving signal.

Moreover, in the active mode, the driving signal can be provided byscanning the conductive strips one at a time until all of the firstconductive strips, all of the second conductive strips or all of theconductive strips (including all of both the first and second conductivestrips) have been provided with the driving signal. Alternatively, aplurality of conductive strips can be provided with the driving signalsimultaneously. For example, the controller may simultaneously providethe driving signal to all of the first conductive strips, all of thesecond conductive strips or all of the conductive strips (including allof both the first and second conductive strips). In a best mode of thepresent invention, the driving signal in the active mode is limited to apredefined frequency, which is not the same as the frequency of thedriving signal in the passive mode. In the passive mode, the location ofan external conductive object can be determined by aforementioned selfcapacitive detection or mutual capacitive detection.

In an example of the present invention, the capacitive pen may include abattery, which can be a dry battery or rechargeable battery, to providethe power necessary for the capacitive pen. In another example of thepresent invention, the capacitive pen may include an internal capacitorthat can temporarily store power, and discharge to provide power to thecapacitive pen. For example, the touch sensor may further include atleast one shielding conductive strip. In the passive mode, the shieldingconductive strip is provided with a DC signal to shield the conductivestrips from external noise interference, whereas in the active mode, theshielding conductive strip is provided with an AC signal. The shieldingconductive strip being provided with the AC signal thus forms a firstcoil that provides an electromagnetic signal. As shown in FIG. 4C, theshielding conductive strip may surround all of the first conductivestrips, all of the second conductive strips or all of the conductivestrips (including all of both the first and second conductive strips).In an example of the present invention, the driving signal received bythe capacitive pen is provided by the electromagnetic signal generatedby the first coil, or by the first coil and some or all of theconductive strips. One with ordinary skill in the art can appreciatethat the power received by the capacitive pen can also be provided byexternal coils of some other forms, for example, by one or more coilsnot surrounding the conductive strips. In an example of the presentinvention, the capacitive pen further includes a second coil. The secondcoil provides the power required for generating the delayed drivingsignal from the signal conversion circuit through electromagneticinduction with the electromagnetic signal of the first coil. Moreover,the aforementioned internal capacitor stores the power produced by thesecond coil via electromagnetic induction.

From the descriptions above, it is clear that the capacitive pen of thepresent invention is particularly suitable for a cordless capacitivepen.

The above embodiments are only used to illustrate the principles of thepresent invention, and they should not be construed as to limit thepresent invention in any way. The above embodiments can be modified bythose with ordinary skill in the art without departing from the scope ofthe present invention as defined in the following appended claims.

What is claimed is:
 1. A cordless capacitive writing device, comprising:a touch sensor including a plurality of conductive strips including aplurality of first conductive strips and a plurality of secondconductive strips; a capacitive pen including a conductive pen head forreceiving a driving signal from the touch sensor and a signal conversioncircuit for generating a delayed driving signal based on the drivingsignal after delaying a predefined period of time, the delayed drivingsignal being transmitted to the touch sensor through the conductive penhead, wherein the driving signal and the delayed driving signal have thesame frequency and phase; and a controller for detecting the location ofat least one external conductive object based on a change in capacitivecoupling of the driving signal between the touch sensor and the at leastone external conductive object in a passive mode, and detecting thelocation of at least one external conductive object based on the delayeddriving signal received from the capacitive pen in an active mode. 2.The cordless capacitive writing device of claim 1, wherein, in thepassive mode, the controller detects the location of the at least oneexternal conductive object at the same time the driving signal is beingprovided, whereas in the active mode, the controller detects thelocation of the capacitive pen in the absence of the driving signal. 3.The cordless capacitive writing device of claim 1, wherein in the activemode, the controller simultaneously provides the driving signal to allof the first conductive strips, all of the second conductive strips, orall of the conductive strips.
 4. The cordless capacitive writing deviceof claim 1, wherein in the active mode, the controller determines afirst one-dimensional (1D) coordinate from signals of the firstconductive strips, and determines a second 1D coordinate from signals ofthe second conductive strips, wherein the first and second 1Dcoordinates form a two-dimensional (2D) coordinate.
 5. The cordlesscapacitive writing device of claim 1, wherein the frequencies of thedriving signal provided in the active mode and the driving signalprovided in the passive mode are different.
 6. The cordless capacitivewriting device of claim 1, wherein the touch sensor further includes ashielding conductive strip provided with a DC signal in the active modeto shield the conductive strips from external noise interference, andprovided with an AC signal in the passive mode, the shielding conductivestrip being provided with the AC signal forms a first coil thatgenerates an electromagnetic signal.
 7. The cordless capacitive writingdevice of claim 6, wherein the capacitive pen further includes a secondcoil for providing power necessary for generating the delayed drivingsignal by the signal conversion circuit through electromagneticinduction with the electromagnetic signal of the first coil.
 8. Thecordless capacitive writing device of claim 6, wherein the drivingsignal received by the capacitive pen is the electromagnetic signalgenerated by the first coil.
 9. The cordless capacitive writing deviceof claim 1, wherein the signal conversion circuit further includes anoscillating feedback loop for generating, based on the driving signal,the delayed driving signal of the same phase as the driving signal,wherein the working frequency of the oscillating feedback loop is thesame as the frequency of the driving signal.
 10. The cordless capacitivewriting device of claim 1, wherein the capacitive pen further includesan internal capacitor for storing the power generated by the second coilthrough electromagnetic induction.